1. Field of the Invention
The present invention relates to a bus arbitration method and a bus arbiter, and more particularly, to a bus arbitration method by which the frequency of bus use can be controlled, a bus arbiter therefor, and a bus system having the bus arbiter.
2. Description of the Related Art
In general, a bus arbiter performs bus arbitration among a plurality of bus masters connected to a bus. Each bus master outputs a request signal to the bus arbiter. The request signal contains information related to the request of use of the bus. The bus arbiter receives the request signal generated by each bus master, and in a predetermined order outputs a grant signal to each bus master. The grant signal contains information granting the use of the bus.
The conventional bus arbiter performs bus arbitration by using either a fixed priority method, or a fairness method, such as a round-robin method. In the fixed priority method, the bus arbiter allocates in advance a different priority to each of a plurality of bus masters, and outputs a grant signal to the bus master having the highest priority. Each priority allocated to one of the plurality of bus masters is generally fixed as a constant value.
The round-robin method is a method by which all elements in one group are fairly selected in a rational order. Generally in the round-robin method, each element is selected one-by-one in the direction from the top of a list to the bottom of the list, when all elements have been selected, then the process again begins with the element at the top of the list. That is, the round-robin method can be understood as a method in which bus opportunities are received by taking turns.
Therefore, for a bus arbiter employing the round-robin method, each bus master fairly uses the bus in a rational order. Consequently, in the case where a predetermined bus master requires preferential use of the bus, the bus master cannot always obtain such preferential use. Also, for a bus arbiter employing the fixed priority method, a bus master having a low priority may not use the bus. These limitations are complicated by the fact that in general, conventional bus arbitration is hard wired in hardware, and therefore is difficult to reconfigure.